The present application relates to diagnostics and prognostics of rotary engine accessories with intermittent duty cycles such as air-conditioner compressors, air compressors, radiator fans, and selectably engageable alternators and pumps, among other such devices. Rotary engine accessories with intermittent duty cycles may experience a variety of failure modes resulting in inconvenience and elevated cost. A variety of diagnostic approaches have been proposed. Yet, conventional proposals suffer from a number of drawbacks, shortcomings and inadequacies relating to diagnostics and prognostics of failures of rotary engine-driven accessories with intermittent duty-cycles. For example, conventional approaches fail to account for the real world operational demand and duty cycles of rotary engine accessories with intermittent duty cycles which significantly constrain and frustrate reliable diagnostics and prognostics. As one example, for commercial on-highway vehicles there is often significant use of the air-conditioner compressor due to the length of the missions and ambient temperatures encountered. In such applications and environments, air-conditioner compressors may experience a relatively high failure rate, creating operator inconvenience and cost issues. Similar issues may be present for a number of other rotary engine accessories with intermittent duty cycles including those noted above. Heretofore, conventional efforts have fallen short of providing a reliable and robust solution to predict or warn the operator ahead of time that rotary engine accessories with intermittent duty cycles are approaching failure or are likely to fail. Reliably predicting component failure in advance of a failure event is desirable to minimize cost effects since failure of one component can lead to damage or failure of associated components damage as well as allowing the operator to get service in a timely manner thereby minimizing operator inconvenience. There remains a substantial need for the unique apparatuses, methods, systems and techniques disclosed herein.